Avian neural crest cell migration is diversely regulated by the two major hyaluronan-binding proteoglycans PG-M/versican and aggrecan

It has been proposed that hyaluronan-binding proteoglycans play an importan t role as guiding cues during neural crest (NC) cell migration, but their p recise function has not been elucidated. In this study, we examine the dist ribution, structure and putative role of the two major hyaluronan-binding p roteoglycans, PG-M/versicans and aggrecan, during the course of avian NC de velopment. PG-M/versicans V0 and V1 are shown to be the prevalent isoforms at initial and advanced phases of NC cell movement, whereas the V2 and V3 t ranscripts are first detected following gangliogenesis. During NC cell disp ersion, mRNAs for PG-M/versicans V0/V1 are transcribed by tissues lining th e NC migratory pathways, as well as by tissues delimiting nonpermissive are as. Immunohistochemistry confirm the deposition of the macromolecules in th ese regions and highlight regional differences in the density of these prot eoglycans. PGM/versicans assembled within the sclerotome rearrange from an initially uniform distribution to a preferentially caudal localization, bot h at the mRNA and protein level. This reorganization is a direct consequenc e of the metameric NC cell migration through the rostral portion of the som ites. hs suggested by previous in situ hybridizations, aggrecan shows a vir tually opposite distribution to PG-M/versicans being confined to the perino tochordal ECM and extending dorsolaterally in a segmentally organized manne r eventually to the entire spinal cord at axial levels interspacing the gan glia. PG-M/versicans purified from the NC migratory routes are highly polyd ispersed, have an apparent M-r of 1,200-2,000 kDa, are primarily substitute d with chondroitin-6-sulfates and, upon chondroitinase ABC digestion, are f ound to be composed of core proteins with apparent Mi of 360-530,000. TEM/r otary shadowing analysis of the isolated PG-M/versicans confirmed that they exhibit the characteristic bi-globular shape, have core proteins with size s predicted for the V0/V1 isoforms and carry relatively few extended glycos aminoglycan chains. Orthotopical implantation of PG-M/versicans immobilized onto transplantable micromembranes tend to 'attract' moving cells toward t hem, whereas similar implantations of a notochordal type-aggrecan retain bo th single and cohorts of moving NC cells in close proximity of the implant and thereby perturb their spatiotemporal migratory pattern. NC cells fail t o migrate through three-dimensional collagen type I-aggrecan substrata in v itro, but locomote in a haptotactic manner through collagen type I-PG-M/ver sican V0 substrata via engagement of HNK-1 antigen-bearing cell surface com ponents. The present data suggest that PG-M/versicans and notochordal aggre can exert divergent guiding functions during NC cell dispersion, which are mediated by both their core proteins and glycosaminoglycan side chains and may involve 'haptotactic-like' motility phenomena. Whereas aggrecan defines strictly impenetrable embryonic areas, PG-M/versicans are central componen ts of the NC migratory pathways favoring the directed movement of the cells .